High energy materials for a battery and methods for making and use

ABSTRACT

A method of forming an electrode active material by reacting a metal fluoride and a reactant. The method includes a coating step and a comparatively low temperature annealing step. Also included is the electrode formed following the method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 14/604,013, having a filing date of Jan. 23, 2015 entitled “High Energy Materials for a Battery and Methods for Making and Use” which is a continuation-in-part of International Application No. PCT/US2014/028506, having an international filing date of Mar. 14, 2014 entitled “High Energy Materials For A Battery And Methods For Making And Use,” which claims priority to U.S. Provisional Application No. 61/786,602 filed Mar. 15, 2013 entitled “High Energy Materials For A Battery And Methods For Making And Use.” This application claims priority to and the benefit of each of these applications, and each application is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention is in the field of battery technology, and more particularly in the area of materials for making high-energy electrodes for batteries, including metal-fluoride materials.

One type of battery consists of a negative electrode made primarily from lithium and a positive electrode made primarily from a compound containing a metal and fluorine. During discharge, lithium ions and electrons are generated from oxidation of the negative electrode while fluoride ions are produced from reduction of the positive electrode. The generated fluoride ions react with lithium ions near the positive electrode to produce a compound containing lithium and fluorine, which may deposit at the positive electrode surface.

Metal fluoride based batteries are an attractive energy storage technology because of their extremely high theoretical energy densities. For example, certain metal fluoride active materials can have theoretical energy densities greater than about 1600 Wh/kg or greater than about 7500 Wh/L. Further, metal fluorides have a relatively low raw material cost, for example less than about $10/kg. However, a number of technical challenges currently limit their widespread use and realization of their performance potential.

One challenge for certain metal fluoride materials is comparatively poor rate performance. Many metal fluoride active materials have electrochemical potentials greater than about 2.5 V because of their relatively large bandgap produced by the highly ionic bonding between the metal and fluorine, and in particular between a transition metal and fluorine. Unfortunately, one of the drawbacks to wide bandgap materials is the intrinsically low electronic conductivity that results from the wide bandgap. As a result of this low conductivity, discharge rates of less than 0.1 C are required in order to obtain full theoretical capacity. More typically, discharge rates of 0.05 C to 0.02 C are reported in the literature. Such low discharge rates limit the widespread use of metal fluoride active materials.

Another challenge for certain metal fluoride active materials is a significant hysteresis observed between the charge and discharge voltages during cycling. This hysteresis is typically on the order of about 1.0V to about 1.5V. While the origin of this hysteresis is uncertain, current evidence suggests that kinetic limitations imposed by low conductivity play an important role. Further, asymmetry in the reaction paths upon charge and discharge may also play a role. Since the electrochemical potential for many of the metal fluorides is on the order of 3.0V, this hysteresis of about 1.0V to about 1.5V limits the overall energy efficiency to approximately 50%.

Limited cycle life is another challenge for certain metal fluoride active materials. Although rechargeability has been demonstrated for many metal fluoride active materials, their cycle life is typically limited to tens of cycles and is also subject to rapid capacity fade. Two mechanisms are currently believed to limit the cycle life for the metal fluoride active materials: agglomeration of metallic nanoparticles and mechanical stress due to volume expansion. It is believed that metal fluoride active materials can cycle by virtue of the formation during lithiation of a continuous metallic network within a matrix of insulating LiF. As the number of cycles increases, the metal particles tend to accumulate together into larger, discrete particles. The larger agglomerated particles in turn create islands that are electrically disconnected from one another, thus reducing the capacity and ability to cycle the metal fluoride active materials. The second limitation to extended cycle life is the mechanical stress imparted to the binder materials by the metal fluoride particles as a result of the volume expansion that occurs during the conversion reaction. Over time, the binder is pulverized, compromising the integrity of the cathode. Notably, for the metal fluoride CuF₂, no demonstrations of rechargeability have been reported.

For CuF₂, an additional challenge prevents rechargeability. The potential required to recharge a CuF₂ electrode is 3.55V. However, in typical electrolytes for lithium ion batteries, Cu metal oxidizes to Cu²⁺ at approximately 3.4 V vs. Li/Li⁺. The oxidized copper can migrate to the anode, where it is irreversibly reduced back to Cu metal. As a result, Cu dissolution competes with the recharge of Cu+2LiF to CuF₂, preventing cycling of the cell. The Cu metal accumulating on the anode surface can increase the impedance and/or destroy the solid-electrolyte interphase (SEI) on the anode.

The following papers and patents are among the published literature on metal fluorides that employ mixed conductors that are not electrochemically active within the voltage window of the metal fluoride: Badway, F. et al., Chem. Mater., 2007, 19, 4129; Badway, F. et al., J. Electrochem. Soc,. 2007, 150, A1318; “Bismuth fluoride based nanocomposites as electrode materials” U.S. Pat. No. 7,947,392; “Metal Fluoride And Phosphate Nanocomposites As Electrode Materials” US 2008/0199772; “Copper fluoride based nanocomposites as electrode materials” US 2006/0019163; and “Bismuth oxyfluoride based nanocomposites as electrode materials” U.S. Pat. No. 8,039,149.

Certain embodiments of the present invention can be used to form electrochemical cells having metal fluoride active material that exhibit improved rate performance, improved energy efficiency, and improved cycle life when compared to prior batteries. Thus, these and other challenges can be addressed by embodiments of the present invention described below.

BRIEF SUMMARY OF THE INVENTION

Certain embodiments of the invention include a method of making a composition for use in forming a cathode for a battery. The method includes coating a metal fluoride material with a coating precursor material including a metal or a metal complex and annealing coated metal fluoride material, wherein at least a portion of the metal fluoride material and at least a portion of the coating undergo a phase change. The metal fluoride material is preferably CuF₂. The metal can be, for example, Ni, Ba, or Ta. The metal complex can be, for example a metal oxide, such as Al₂O₃, SiO₂, Ta₂O₅, TiO₂; a metal nitride, such as AlN, TaN; a metal silicate, such as ZrSiO₄; or other materials that are volatile enough to be evaporated and re-condensed onto a substrate. The annealing temperature is less than 450 degrees C., less than 400 degrees C., less than 325 degrees C., or less than 200 degrees C. Preferably, the annealing temperature is about 325 degrees C. The temperature is chosen such that it is sufficiently high for the metal complex to react with the metal fluoride, but not high enough to decompose the metal fluoride. Without such heat treatment and the resulting reaction, the material is not rechargeable, as is demonstrated by experiments described herein.

Certain embodiments of the invention include a composition formed by the methods disclosed herein. The composition is characterized by having reversible capacity. The composition can include particles with a grain size greater than 100 nm, 110 nm, 120 nm, or 130 nm. The composition can include a particle having a first phase and a coating on the particle having a second phase. Preferably, the first phase includes the metal fluoride and the second phase includes the metal oxide. The coating can be covalently bonded to the particle.

Certain embodiments of the invention include batteries having electrodes formed from the compositions disclosed herein, the method of making such batteries, and the method of use of such batteries.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates electrochemical characterization of different hybrid cathode formulations according to embodiments of the invention in which the content of a conductive precursor material is varied in the cathode.

FIG. 2 illustrates electrochemical characterization of a cathode formulation from FIG. 1 in which the voltage of a hybrid cathode according to embodiments of the invention is plotted against the capacity for the first and second cycles.

FIG. 3 illustrates electrochemical characterization of different hybrid cathode formulations according to embodiments of the invention in which the discharge is plotted as a function of cycle for 10 cycles.

FIG. 4 illustrates electrochemical characterization of a hybrid cathode formed from a metal fluoride and a reactant material according to certain embodiments. The cathode demonstrates rechargeability.

FIG. 5 illustrates a powder X-ray diffraction pattern of a material used to form a rechargeable metal fluoride cathode.

FIG. 6 illustrates second cycle discharge capacity for a variety of hybrid cathode materials used according to embodiments of the invention.

FIG. 7 illustrates second cycle discharge capacity for a hybrid cathode material used according to embodiments of the invention versus annealing temperature.

FIG. 8 illustrates second cycle the capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt % CuF₂ with 15 wt % of certain metal oxides (in this case NiO or TiO₂) at certain annealing temperatures.

FIG. 9 illustrates the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt % CuF₂ with 15 wt % of certain metal oxides (in this case NiO or TiO₂) for certain annealing times.

FIG. 10 illustrates the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt %, 90 wt %, or 95 wt % CuF₂ with 5 wt %, 10 wt %, 15 wt % of NiO.

FIG. 11 illustrates the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO as a function of milling energy.

FIG. 12 illustrates the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO as a function of milling time.

FIG. 13 illustrates the second cycle reversible capacity measured for various starting materials used to react with CuF₂.

FIG. 14 illustrates the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting CuF₂ with nickel (II) acetylacetonate using various processing conditions.

FIG. 15 illustrates the capacity as a function of cycle for cathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO and for a control material.

FIG. 16 illustrates a galvanostatic intermittent titration technique measurement for cathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO.

FIG. 17 illustrates the capacity of full cells and half cells as a function of cycle for cathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO.

FIG. 18 illustrates voltage traces of the full cell and half cells prepared as described in relation to FIG. 17.

FIG. 19 illustrates the capacity retention of full cells and half cells as a function of cycle for cathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO.

FIG. 20 illustrates the second cycle reversible capacity measured for various coating precursor materials used to react with CuF₂.

DETAILED DESCRIPTION OF THE INVENTION

The following definitions apply to some of the aspects described with respect to some embodiments of the invention. These definitions may likewise be expanded upon herein. Each term is further explained and exemplified throughout the description, figures, and examples. Any interpretation of the terms in this description should take into account the full description, figures, and examples presented herein.

The singular terms “a,” “an,” and “the” include the plural unless the context clearly dictates otherwise. Thus, for example, reference to an object can include multiple objects unless the context clearly dictates otherwise.

The terms “substantially” and “substantial” refer to a considerable degree or extent. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation, such as accounting for typical tolerance levels or variability of the embodiments described herein.

The term “about” refers to the range of values approximately near the given value in order to account for typical tolerance levels, measurement precision, or other variability of the embodiments described herein.

The terms “conductive,” “conductor,” “conductivity,” and the like refer to the intrinsic ability of a material to facilitate electron or ion transport and the process of doing the same. The terms include materials whose ability to conduct electricity may be less than typically suitable for conventional electronics applications but still greater than an electrically-insulating material.

The term “active material” and the like refers to the material in an electrode, particularly in a cathode, that donates, liberates, or otherwise supplies the conductive species during an electrochemical reaction in an electrochemical cell.

The term “transition metal” refers to a chemical element in groups 3 through 12 of the periodic table, including scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury (Hg), rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), hassium (Hs), and meitnerium (Mt).

The term “halogen” refers to any of the chemical elements in group 17 of the periodic table, including fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).

The term “chalcogen” refers to any of chemical elements in group 16 of the periodic table, including oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and polonium (Po).

The term “alkali metal” refers to any of the chemical elements in group 1 of the periodic table, including lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

The term “alkaline earth metals” refers to any of the chemical elements in group 2 of the periodic table, including beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

The term “rare earth element” refers to scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).

A rate “C” refers to either (depending on context) the discharge current as a fraction or multiple relative to a “1 C” current value under which a battery (in a substantially fully charged state) would substantially fully discharge in one hour, or the charge current as a fraction or multiple relative to a “1 C” current value under which the battery (in a substantially fully discharged state) would substantially fully charge in one hour.

In certain embodiments, a novel active material is prepared for use in a cathode with metal fluoride (MeF_(x)) active materials. In some embodiments, the novel active material, sometimes referred to herein as a hybrid material, is prepared by combining a metal fluoride and a metal complex, followed by heat treatment of the mixture under an inert atmosphere according to the Formula (I)

MeF_(x)+Me′_(y)X_(z)+heat   (I)

According to certain embodiments, the heat treatment of the metal fluoride and metal complex causes a reaction to form a new phase according to the formula (II)

MeF_(x)+Me′_(y)X_(z)→Me_(a)Me′_(b)X_(c)F_(d)   (II)

where x, y, z, a, b, and c depend on the identity and valence of the Me, Me′, and X. In some instances, 0<a≦1, 0<b≦1, 0≦c≦1, and 0≦d≦1. In other embodiments, the heat treatment causes the formation of covalent bonds between the metal fluoride and the metal complex, improving conductivity and passivating the surface.

Suitable metal complexes, which can act as precursors for the reaction described herein, for use in synthesizing the active material include, but are not limited to, MoO₃, MoO₂, NiO, CuO, VO₂, V₂O₅, TiO₂, Al₂O₃, SiO₂, LiFePO₄, LiMe_(T)PO₄ (where Me_(T) is one or more transition metal(s)), metal phosphates, and combinations thereof. According to embodiments of the invention, these oxides can be used in Formula (I).

It is understood that the synthetic route for achieving the active material may vary, and other such synthetic routes are within the scope of the disclosure. The material can be represented by Me_(a)Me′_(b)X_(c)F and in the examples herein is embodied by a Cu₃Mo₂O₉ active material. Other active materials are within the scope of this disclosure, for example, NiCuO₂, Ni₂CuO₃, and Cu₃TiO₄.

The coating materials disclosed herein provide rechargeability to otherwise non-rechargeable metal fluoride materials. Without being bound by a particular theory or mechanism of action, the rechargeability may be due to the electrochemical properties of the novel hybrid material, the coating of the metal fluoride to prevent copper dissolution, or a more intimate interface between the metal fluoride and the coating material as a result of the heat treatment and reaction. Further, the novel hybrid material may provide a kinetic barrier to the Cu dissolution reaction, or to similar dissolution reactions for other metal fluoride materials to the extent such dissolution reactions occur in the cycling of electrochemical cells.

In the case of oxide-based hybrid materials, intimate mixing of the metal fluoride and the metal complex (or other suitable precursor material) and moderate heat treatment can be used to generate rechargeable electrode materials. Suitable coating precursors include materials that decompose to form metal oxides (and in particular, transition metal oxides) as opposed to using a metal oxide to directly react with the metal fluoride. Examples of such precursors include, but are not limited to, metal acetates, metal acetylacetonates, metal hydroxides, metal ethoxides, and other similar organo-metal complexes. In either event, the final rechargeable material is not necessarily a pure oxide or a purely crystalline material. The reaction of Formula II predicts that there would not be a pure oxide or a purely crystalline material. In some instances, the metal oxide precursor or metal oxide material can form a coating, or at least a partial coating, on the metal fluoride active material. Without being bound by a particular theory or mechanism of action, the reaction of the metal oxide precursor or metal oxide material with the surface of the metal fluoride (and in particular copper fluoride) active material is important for generating a rechargeable electrode active material.

EXAMPLES

The following examples describe specific aspects of some embodiments of the invention to illustrate and provide a description for those of ordinary skill in the art. The examples should not be construed as limiting the invention, as the examples merely provide specific methodology useful in understanding and practicing some embodiments of the invention.

Example 1 Fabrication of Hybrid and/or Coated Electrodes for Rechargeable Cells

Materials and Synthetic Methods. All reactions were prepared in a high purity argon filled glove box (M-Braun, O₂ and humidity contents <0.1 ppm). Unless otherwise specified, materials were obtained from commercial sources (e.g., Sigma-Aldrich, Advanced Research Chemicals Inc., Alfa Aesar, Strem) without further purification.

Preparation of CuF₂ Hybrid. Milling vessels were loaded with CuF₂ at from about 85 wt % to about 95 wt % and reactant (metal oxide or metal oxide precursor) at from about 5 wt % to about 15 wt %, and the vessels were sealed. The mixture was milled. After milling, samples were annealed at from about 200 degrees C. to about 575 degrees C. for 1 to 12 hours under flowing N₂. Specific hybrid-forming reactants were processed as described below.

Preparation of CuF₂/Cu₃Mo₂O₉. Milling vessels were loaded with CuF₂ (85 wt %) and MoO₃ (15 wt %), sealed, and then milled. After milling, samples were annealed at 450 degrees C. for 6 hours under flowing N₂.

Preparation of CuF_(2/)NiO. Milling vessels were loaded with CuF₂ (85 wt %) and NiO (15 wt %), sealed, and then milled. After milling, samples were annealed at 325 degrees C. for 6 hours under flowing N₂.

Preparation of CuF_(2/)Nickel (II) acetylacetonate. A fine dispersion of CuF₂ was prepared by milling in the presence of THF (40-120 mg CuF₂/mL THF). The dispersed sample was then added to a solution of Ni(AcAc)₂ in THF such that Nickel (II) acetylacetonate accounted for 15 wt % of the solids in the solution. The solution was then agitated by either shaking, sonication, or low energy milling for from about 1 to about 12 hours. The solution was then dried at room temperature under vacuum and the resulting solid was annealed at 450 degrees C. for 6 hours under dry air.

Preparation of Vapor Deposited Coatings The coating material (nickel metal) was vaporized and then physically condensed onto the substrate at 20 weight percent. X-ray diffraction measurements were performed on the coated material to confirm the bulk CuF₂ was not altered. The coated material was then annealed similarly to materials prepared by other methods.

Preparation of Atomic Layer Deposited Coatings CuF₂ was coated with TiO₂ by atomic layer deposition methods. The expected coating thickness was about 8.5 nm based on ellipsometry measurements on a silicon witness sample, which represented a nominal 3 weight percent coating on the CuF₂. The coated material was then annealed similarly to materials prepared by other methods.

Electrode Formulation. Cathodes were prepared using a formulation composition of 80:15:5 (active material:binder:conductive additive) according to the following formulation method: 133 mg PVDF (Sigma Aldrich) and about 44 mg Super P Li (Timcal) was dissolved in 10 mL NMP (Sigma Aldrich) overnight. 70 mg of coated composite powder was added to 1 mL of this solution and stirred overnight. Films were cast by dropping about 70 μL of slurry onto stainless steel current collectors and drying at 150 degrees C. for about 1 hour. Dried films were allowed to cool, and were then pressed at 1 ton/cm². Electrodes were further dried at 150 degrees C. under vacuum for 12 hours before being brought into a glove box for battery assembly.

Example 2 Electrochemical Characterization of Electrochemical Cells Containing Rechargeable Electrodes

All batteries were assembled in a high purity argon filled glove box (M-Braun, O₂ and humidity contents <0.1 ppm), unless otherwise specified. Cells were made using lithium as an anode, Celgard 2400 separator, and 90 μL of 1M LiPF₆ in 1:2 EC:EMC electrolyte. Electrodes and cells were electrochemically characterized at 30 degrees C. with a constant current C/50 charge and discharge rate between 4.0 V and 2.0 V. A 3 hour constant voltage step was used at the end of each charge. In some instances, cathodes were lithiated pressing lithium foil to the electrode in the presence of electrolyte (1M LiPF₆ in 1:2 EC:EMC) for about 15 minutes. The electrode was then rinsed with EMC and built into cells as described above, except graphite was used as the anode rather than lithium.

FIG. 1 illustrates the results of electrochemical characterization of certain embodiments disclosed herein. Specifically, the second cycle discharge capacity of three different cathode formulations containing a LiFePO₄ material is plotted as a function of LiFePO₄ content (labeled LFP) in the cathode in FIG. 1. The dotted line depicts the theoretical capacity of LiFePO₄. One cathode formulation is 100% LiFePO₄. Another cathode formulation is a combination of CuF₂ and LiFePO₄ in which the content of LiFePO₄ was varied from 10% to 50% of the total weight of conductive material. The third cathode formulation is a combination of CuF₂ and the conventional conductive oxide MoO₃ and LiFePO₄ in which the content of LiFePO₄ was varied from 10% to 50% of the total weight of conductive material. As this is second cycle data, FIG. 1 demonstrates that all of the CuF₂/LiFePO₄ matrices are rechargeable. In addition, the (CuF₂/MoO₃)/LiFePO₄ hybrid cathode containing 50% LiFePO₄ is also able to recharge. FIG. 1 further demonstrates a direct relationship between the capacity and the percent content of LiFePO₄.

FIG. 2 illustrates the results of electrochemical characterization of certain embodiments disclosed herein. Specifically, the voltage of a hybrid cathode is plotted against the capacity for the first and second cycles. The dashed line indicates the expected theoretical capacity from the LiFePO₄ content in cathode. The cathode formulation is the CuF₂ (70%)/LiFePO₄ (30%) hybrid cathode from FIG. 1. During the first cycle, very little discharge capacity is observed, indicating that the LiFePO₄ material is not capable of accepting charge on this cycle. Without being bound to a particular theory or mechanism of action, the LiFePO₄ material may not accept charge as a result of defects introduced during milling. This data suggests that all of the capacity observed during the first and second cycles can be attributed solely to the CuF₂.

FIG. 3 illustrates the results of electrochemical characterization of certain embodiments disclosed herein. Specifically, the discharge capacity for cells with a range of LiFePO₄ content is plotted as a function of cycle for 10 cycles. The cathode formulation is CuF₂ with LiFePO₄ content ranging from 10% to 50% of the total weight of conductive material. FIG. 4 demonstrates that the hybrid cathode is able to consistently recharge across a number of cycles. Based on data from FIG. 2, it is expected that the discharge capacity is contributed solely by CuF₂ and not LiFePO₄. This is a significant finding because CuF₂ has not been previously shown to have such significant reversible capacity. The combination of certain conductive materials with CuF₂ renders the CuF₂ cathode material rechargeable.

FIG. 4 illustrates the results of electrochemical characterization of certain embodiments disclosed herein. Specifically, the first and second cycle voltage traces for a cell containing a cathode formed from a metal fluoride and the new hybrid material. In this case, the metal fluoride active material is CuF₂ and the hybrid material is Cu₃Mo₂O₉. FIG. 4 demonstrates that the cell has about 140 mAh/g of reversible capacity. Previously known cathodes containing CuF₂ have not demonstrated such significant reversible capacity.

FIG. 5 illustrates the results of structural characterization of certain embodiments disclosed herein. Specifically, the powder X-ray diffraction pattern of the material forming the cathode tested in FIG. 4 is shown along with the powder X-ray diffraction patterns of CuF₂ and Cu₃Mo₂O₉. FIG. 5 demonstrates that the material contains phases rich in CuF₂ and phases rich in Cu₃Mo₂O₉. Thus, FIG. 5 demonstrates a new hybrid material in combination with a metal fluoride active material. Further, grain size analysis of this powder X-ray diffraction data shows that the CuF₂ has a grain size greater than 130 nm. This is a significant finding since such comparatively large particles were thought to be too large to provide good electrochemical performance.

For many of the rechargeable matrices described herein (and in particular for matrices including Mo, Ni, or Ti), the reactions described herein yield a new material at least at the surface of the particles of the metal fluoride active material. The novel material present at least at the surface of the particles of the metal fluoride active material is believed to provide many of the benefits disclosed herein.

FIG. 6 illustrates the results of electrochemical characterization of certain embodiments disclosed herein. Specifically, the second cycle discharge capacity of CuF₂ with various materials and annealing temperatures. FIG. 6 shows many oxide materials that provide recharge capability, demonstrated by capacities greater than 100 mAh/g.

Table 1 presents the results of further electrochemical characterization of certain embodiments disclosed herein. Table 1 shows that many metal oxide and metal oxide precursor starting materials can be used in the reactions described herein to yield rechargeable metal fluoride electrode materials. The materials in Table 1 include metal oxides, metal phosphates, metal fluorides, and precursors expected to decompose to oxides. In particular, nickel oxide showed excellent performance.

TABLE 1 Electrochemical Characterization of Various Precursor Materials as a Function of Anneal Temperature Initial Capacity Reversible Precursor Annealing Temp (0.02 C, Cy1, Capacity (0.05 C, Material (C.) mAh/g) Cy2, mAh/g) None 200 181 30 None 325 394 216 None 450 247 61 (NH₄)H₂PO₄ 200 307 5 (NH₄)H₂PO₄ 325 406 178 (NH₄)H₂PO₄ 450 397 0 Al₂O₃ 200 281 70 Al₂O₃ 325 348 107 Al₂O₃ 400 203 78 AlF₃ 200 397 124 AlF₃ 325 384 125 AlF₃ 400 320 98 AlPO₄ 200 410 115 AlPO₄ 325 356 136 AlPO₄ 450 284 74 Bi₂O₃ 200 128 32 Bi₂O₃ 325 89 34 Bi₂O₃ 400 103 36 CaF₂ 200 301 86 CaF₂ 325 310 107 CaF₂ 400 282 125 CaO 200 1 1 CaO 325 138 27 CaO 400 84 29 Co₃(PO₄)₂ 200 323 93 Co₃(PO₄)₂ 325 373 161 Co₃(PO₄)₂ 450 382 126 Co₃O₄ 200 167 112 Co₃O₄ 325 216 132 Co₃O₄ 450 329 151 Co₃O₄ 575 310 134 Cr₂O₃ 200 223 88 Cr₂O₃ 325 234 132 Cr₂O₃ 450 227 102 Cr₂O₃ 575 184 70 Fe Acetate 200 407 31 Fe Acetate 325 431 11 Fe Acetate 450 393 180 Fe₂O₃ 200 197 135 Fe₂O₃ 325 200 142 Fe₂O₃ 450 170 112 Fe₂O₃ 575 308 131 FeF₂ 200 427 202 FeF₂ 325 382 220 FeF₂ 400 370 155 FeF₃ 200 443 188 FeF₃ 325 406 218 FeF₃ 400 359 141 FePO₄ 200 252 76 FePO₄ 325 393 147 FePO₄ 450 429 197 In₂O₃ 200 250 64 In₂O₃ 325 203 106 In₂O₃ 400 347 109 La₂O₃ 200 281 74 La₂O₃ 325 155 39 La₂O₃ 450 68 29 La₂O₃ 575 114 36 Li₂O 200 32 11 Li₂O 325 49 18 Li₂O 400 38 18 Li₃PO₄ 200 318 123 Li₃PO₄ 325 435 136 Li₃PO₄ 450 409 114 LiCoPO₄ 200 372 97 LiCoPO₄ 325 408 142 LiCoPO₄ 450 338 136 LiH₂PO₄ 200 300 111 LiH₂PO₄ 325 423 149 LiH₂PO₄ 450 387 107 LiMnPO₄ 200 351 77 LiMnPO₄ 325 368 102 LiMnPO₄ 450 397 178 LiNiPO₄ 200 402 116 LiNiPO₄ 325 396 191 LiNiPO₄ 450 405 176 MgF₂ 200 387 135 MgF₂ 325 378 147 MgF₂ 400 360 122 MgO 200 313 181 MgO 325 259 155 MgO 400 198 126 MnO 200 117 52 MnO 325 130 65 MnO 450 83 55 MnO 575 59 38 MnO₂ 200 120 76 MnO₂ 325 123 57 MnO₂ 450 242 150 MnO₂ 575 104 69 Mo Acetate 200 396 10 Mo Acetate 325 433 17 Mo Acetate 450 398 46 Na₂O 200 2 1 Na₂O 325 26 13 Na₂O 400 24 13 Ni 200 345 197 Ni 325 301 178 Ni 400 302 158 Ni 450 300 152 Ni acac 200 425 56 Ni acac 325 306 87 Ni Acac 400 247 30 Ni acac 450 362 172 Ni acetate 200 397 148 Ni acetate 325 376 46 Ni acetate 350 370 191 Ni acetate 400 383 180 Ni acetate 450 371 186 Ni acetate 500 373 171 Ni₃(PO₄)₂ 200 410 124 Ni₃(PO₄)₂ 325 430 52 Ni₃(PO₄)₂ 450 126 44 Ni(C₂O₂) 200 359 90 Ni(C₂O₂) 325 395 195 Ni(C₂O₂) 450 381 175 Ni(CP)₂ 200 304 27 Ni(CP)₂ 325 317 14 Ni(CP)₂ 450 258 148 Ni(OH)₂ 200 412 186 Ni(OH)₂ 325 362 196 Ni(OH)₂ 400 327 181 Ni(OH)₂ 450 300 169 NiBr₂ 200 125 0 NiBr₂ 325 225 78 NiBr₂ 400 244 113 NiCO₃*Ni(OH)₂ 200 380 17 NiCO₃*Ni(OH)₂ 325 359 215 NiCO₃*Ni(OH)₂ 450 317 184 NiF₂ 200 367 121 NiF₂ 325 395 207 NiF₂ 400 411 170 NiF₂ 450 396 177 NiO 125 257 131 NiO 200 403 222 NiO 225 384 212 NiO 250 385 221 NiO 275 370 229 NiO 300 335 175 NiO 325 402 252 NiO 350 365 209 NiO 375 260 123 NiO 400 371 200 NiO 425 361 186 NiO 450 386 183 NiO 500 308 150 NiO 575 319 112 Sb₂O₃ 200 111 34 Sb₂O₃ 325 147 37 Sb₂O₃ 400 223 104 Sc₂O₃ 200 359 159 Sc₂O₃ 325 293 159 Sc₂O₃ 400 84 33 Sc₂O₃ 450 150 68 Sc₂O₃ 575 55 17 ScF₃ 200 400 178 ScF₃ 325 387 174 ScF₃ 400 243 100 SiO₂ 200 1 1 SiO₂ 325 114 28 SiO₂ 400 230 92 SnO₂ 200 210 48 SnO₂ 325 182 68 SnO₂ 400 133 65 SrO 200 152 12 SrO 325 66 16 SrO 400 134 48 Ta₂O₅ 200 289 4 Ta₂O₅ 325 269 141 Ta₂O₅ 450 298 121 Ta₂O₅ 575 317 74 Ti(OEt)₄ 200 438 21 Ti(OEt)₄ 325 453 12 Ti(OEt)₄ 450 353 5 TiO₂ 225 322 150 TiO₂ 250 309 169 TiO₂ 275 262 162 TiO₂ 300 199 127 TiO₂ 325 322 173 TiO₂ 350 327 187 TiO₂ 375 120 77 TiO₂ 400 359 199 TiO₂ 425 345 194 TiO₂ 450 353 169 Y₂O₃ 200 353 130 Y₂O₃ 325 279 104 Y₂O₃ 450 83 37 Y₂O₃ 575 80 30 ZnF₂ 200 438 206 ZnF₂ 325 372 191 ZnF₂ 400 318 134 ZnO 200 210 95 ZnO 325 242 93 ZnO 400 194 44 ZnO 450 205 99 ZnO 575 151 71 ZrO₂ 200 302 122 ZrO₂ 325 288 129

FIG. 7 illustrates the results of electrochemical characterization of certain embodiments disclosed herein. Specifically, the second cycle discharge capacity for cells containing a cathode formed from a metal fluoride and the precursor material treated at different temperatures. In this case, the metal fluoride active material is CuF₂ and the precursor material is NiO. FIG. 7 shows a peak for cycle 2 capacity at about 325 degrees C. for NiO precursors, with nearly 250 mAh/g discharge capacity.

FIG. 8 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt % CuF₂ with 15 wt % of certain metal oxides (in this case NiO or TiO₂) at certain annealing temperatures. The mixtures were milled at high energy for about 20 hours. The anneal temperatures ranged from about 225 degrees C. to about 450 degrees C. and the anneal time was 6 hours. The 325 degree C. anneal temperature for the NiO starting material generated the best performance. The cells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed at a rate of 0.02 C and over a voltage range of 2.0 V to 4.0 V.

FIG. 9 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt % CuF₂ with 15 wt % of certain metal oxides (in this case NiO or TiO₂) for certain annealing times. The mixtures were milled at high energy for about 20 hours. The anneal temperature was 325 degrees C. and the anneal time was 1 hour, 6 hours, or 12 hours. The 6 hour anneal time yielded the best results for both the NiO and TiO₂ starting materials, and the NiO starting material generated better performance. The cells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed at a rate of 0.02 C and over a voltage range of 2.0 V to 4.0 V.

FIG. 10 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt %, 90 wt %, or 95 wt % CuF₂ with 5 wt %, 10 wt %, 15 wt % of NiO. The mixtures were milled at high energy for about 20 hours. The anneal temperature was 325 degrees C. and the anneal time was 6 hours. Using 10 wt % or 15 wt % of the NiO starting material generated better performance. The cells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed at a rate of 0.02 C and over a voltage range of 2.0 V to 4.0 V.

FIG. 11 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO. The mixtures were milled at various energies comparable to milling on a Fritch Pulverisette 7 Planatery Mill at 305, 445, 595, and 705 RPM for about 20 hours. The anneal temperature was 325 degrees C. and the anneal time was 6 hours. Performance improves with increasing milling energy, suggesting that intimate physical interaction of the materials is required. The cells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed at a rate of 0.05 C and over a voltage range of 2.0 V to 4.0 V.

FIG. 12 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO. The mixtures were milled for various times (3 hours, 20 hours, or 40 hours) at a high energy (comparable to 705 RPM on Fritch Pulverisette 7). The anneal temperature was 325 degrees C. and the anneal time was 6 hours. Performance does not improve after 20 hours of milling. The cells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed at a rate of 0.05 C and over a voltage range of 2.0 V to 4.0 V.

FIG. 13 illustrates the results of electrochemical characterization of certain embodiments disclosed herein. Specifically, FIG. 13 shows the second cycle reversible capacity measured for various starting materials used to react with CuF₂. The starting materials include NiO, nickel (II) acetylacetonate (Ni acac in Table 1), nickel acetate, nickel hydroxide, NiCO₃*Ni(OH)₂, Ni(C₂O₂), Ni(CP)₂, and Ni. In some instances, the starting materials react to form a new phase. The materials react with the surface of the CuF₂ particles. Additionally, the anneal atmosphere was either N₂ or dry air. The precursor starting materials decompose to NiO (although this depends on the atmosphere for some precursors) at or below the annealing temperatures used for the reaction. The precursors that are soluble or have low boiling points can enable solution or vapor deposition processing methods. The cells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed at a rate of 0.05 C and over a voltage range of 2.0 V to 4.0 V. Several materials show similar performance to the NiO baseline.

FIG. 14 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting CuF₂ with nickel (II) acetylacetonate using various processing conditions. In some cases, the CuF₂ was dispersed using methods described herein. The coatings were applied using mill coating techniques (that is, agitating the mixture in a milling apparatus) or by solution coating techniques (including solution coating driven by physisorption). All samples were annealed under dry air. The cells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed at a rate of 0.05 C and over a voltage range of 2.0 V to 4.0 V. Testing demonstrates that solution coating methods can provide similar performance to the mill coating techniques.

FIG. 20 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the second-cycle capacity retention and reversible capacity for cathode active materials formed from reacting CuF₂ with coatings formed from various coating methods and from various precursors. The precursors included NiO, Ni, TiO₂, nickel (II) acetylacetonate, and nickel acetate. All five precursor types were applied according to the mill coating techniques (that is, agitating the mixture in a milling apparatus). Solution coating techniques were used for nickel (II) acetylacetonate, and nickel acetate. Physical vapor deposition (PVD) techniques were used to form a coating from Ni precursor, and atomic layer deposition (ALD) techniques were used to form a coating from TiO₂. All samples were annealed under dry air. The cells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed at a rate of 0.05 C and over a voltage range of 2.0 V to 4.0 V.

The solution, vapor, and atomic layer deposition methods can provide comparatively more uniform coatings on metal fluoride particles than the coatings obtained by milling methods. A comparatively thinner, more uniform coatings can provide the benefits of the coating material, such as more complete protection of the metal fluoride particle, with less precursor material. To the extent that excess precursor material is less active (and therefore less desirable) than the active material, thin, conformal coatings can provide an advantage in terms of weight-normalized reversible capacity.

FIG. 20 shows that although absolute reversible capacity was inferior for solution and vapor coatings as compared to milled coatings, the reversible capacity per weight percentage of coating was significantly improved. For example, for the TiO₂ the atomic layer deposition coating method yielded greater than about 60% more reversible capacity per coating weight than the milled coating method. The ALD coated material had a coating that was about 8 nm thick and less than about 3 weight percent of the coated particle.

Notably, the non-milling coating methods shown in FIG. 20 (that is, the solution coating, vapor deposition, and atomic layer deposition methods) are compatible with a subset of the metal complexes disclosed herein. A variety of coating materials is possible with atomic layer deposition methods including metals (e.g., Ni), metal oxides (e.g., Al₂O₃, SiO₂, Ta₂O₅, TiO₂), metal nitrides (e.g., AlN, TaN), and others. Physical vapor deposition techniques can also deposit coatings of a wide number of materials including metals (e.g., Ni, Ba, Ta), metal oxides (e.g., SiO₂, Ta₂O₅, TiO₂, NiO), metal nitrides (e.g., TiN, AlN), metal silicates (e.g., ZrSiO₄) or other materials that are volatile enough to be evaporated and re-condensed onto a substrate.

FIG. 15 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the capacity as a function of cycle for cathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO and for a control material. The NiO/CuF₂ mixture was milled at high energy for about 20 hours. The anneal temperature was 325 degrees C. and the anneal time was 6 hours. The cells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed at a cycle 1 rate of 0.02 C, a cycle 2 rate of 0.05 C, and a cycle 3 through cycle 25 rate of 0.5 C and over a voltage range of 2.0 V to 4.0 V. With the reacted NiO/CuF₂ as the active material, the cell cycles reversibly for extended cycling with capacity greater than 100 mAh/g for 25 cycles. Further, the reacted NiO/CuF₂ active material demonstrates retention of 80% of cycle 3 capacity as far out as cycle 15. The control material, which was prepared according to the process described in Badway, F. et al., Chem. Mater., 2007, 19, 4129, does not demonstrate any rechargeable capacity. Thus, the material prepared according to embodiments described herein is significantly superior to known materials processed according to known methods.

FIG. 16 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, a galvanostatic intermittent titration technique (GITT) measurement for cathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO and for a control material. The NiO/CuF₂ mixture was milled at high energy for about 20 hours. The anneal temperature was 325 degrees C. and the anneal time was 6 hours. The cells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed over a voltage range of 2.0 V to 4.0 V at a rate of 0.1 C and with a 10 hour relaxation time. The GITT measurement relaxation points show low voltage hysteresis (about 100 mV), which indicate that the overpotential and/or underpotential are likely caused by kinetic and not thermodynamic limitations. This is consistent with other properties and characteristics observed for the reacted NiO/CuF₂ active material.

FIG. 17 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the capacity of full cells and half cells as a function of cycle for cathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO. The NiO/CuF₂ mixture was milled at high energy for about 20 hours. The anneal temperature was 325 degrees C. and the anneal time was 6 hours. The label “Cu+2LiF” indicated that the NiO/CuF₂ electrode was lithiated by pressing Li foil to CuF₂ electrode in the presence of electrolyte as described above. The other half cell was lithiated electrochemically in the initial cycles. The cells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed over a voltage range of 2.0 V to 4.0 V. Half cell performance is essentially identical between the two lithiation methods after cycle 2, while full cell shows additional irreversible capacity loss as compared to the half cells but similar capacity retention.

FIG. 18 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the voltage traces of the full cell and half cells prepared as described in relation to FIG. 17. The full cell has similar charge capacity to the half cells, but larger irreversible capacity loss and lower discharge voltage (which can indicate increased cell impedance). FIG. 18 demonstrates that the full cell has about 250 mAh/g of reversible capacity and about 500 mV hysteresis between charge and discharge plateau voltages.

FIG. 19 illustrates the results of electrochemical characterization of certain embodiments disclosed herein, specifically, the capacity retention of full cells and half cells as a function of cycle for cathode active materials formed from reacting 85 wt %, CuF₂ with 15 wt % of NiO. The results from a control material are also depicted. The full cell and half cells were prepared as described in relation to FIG. 17. The cells used a Li anode and an electrolyte containing 1M LiPF₆ in EC:EMC. The testing was performed at a cycle 1 rate of 0.1 C and over a voltage range of 2.0 V to 4.0 V. The capacity retention is essentially identical for the full and half cells of the NiO/CuF₂ active material. The control material shows essentially no rechargeable capacity.

While the invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, or process to the objective, spirit and scope of the invention. All such modifications are intended to be within the scope of the claims appended hereto. In particular, while the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the invention. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not limitations of the invention. 

We claim:
 1. A method of making an electrode, comprising: coating particles, wherein each particle includes a metal fluoride material, with a coating precursor material, wherein the coating precursor material includes a transition metal; annealing the particles such that at least a portion of the metal fluoride material and at least a portion of the transition metal react to undergo a phase change; and forming the coated particles into an electrode.
 2. The method of claim 1, wherein the electrode forming step comprises preparing a formulation composition of coated particles, binder, and conductive additive.
 3. The method of claim 1, wherein the metal fluoride material comprises copper fluoride.
 4. The method of claim 1, wherein the coating step comprising milling the particles with the coating precursor material.
 5. The method of claim 4, wherein the coating precursor material comprises a organo-metal complex.
 6. The method of claim 4, wherein the coating precursor material comprises a metal oxide.
 7. The method of claim 4, wherein the coating precursor material comprises elemental metal.
 8. The method of claim 4, wherein the coating precursor material comprises NiO.
 9. The method of claim 4, wherein the coating precursor material comprises TiO₂.
 10. The method of claim 4, wherein the coating precursor material is Ni.
 11. The method of claim 4, wherein the coating precursor material comprises nickel (II) acetylacetonate.
 12. The method of claim 4, wherein the coating precursor material comprises nickel acetate.
 13. The method of claim 1, wherein the coating step comprises a solution coating process.
 14. The method of claim 13, wherein the coating precursor material comprises an organo-metal complex.
 15. The method of claim 13, wherein the coating precursor material comprises nickel (II) acetylacetonate.
 16. The method of claim 1, wherein the coating step comprises a physical vapor deposition process.
 17. The method of claim 16, wherein the coating precursor material comprises a metal oxide.
 18. The method of claim 16, wherein the coating precursor material comprises a metal nitride.
 19. The method of claim 16, wherein the coating precursor material comprises a metal silicate.
 20. The method of claim 16, wherein the coating precursor material is Ni or Ti. 